SURFACE PHOTOVOLTAGE IN SEMICONDUCTORS UNDER PULSED OPTICAL-EXCITATION, AND ITS RELEVANCE TO SYNCHROTRON-RADIATION SPECTROSCOPY

We used the SuperACO Free Electron Laser (FEL) to excite photocarriers in semiconductors at room temperature, and synchrotron radiation phot oemission spectroscopy to measure the consequently induced surface pho tovoltage (SPV), The natural synchronization between the two sources a llowed us to study with sub-nanosecond resolution the temporal depende nce of the non-equilibrium charge carrier distribution for two prototy pe systems, Ag/GaAs(110) and Si(111)2 x 1. We found that to correctly interpret the effects of the SPV on the band position, the interplay b etween instrumental factors (pulse duration and repetition rate) and s emiconductor parameters (such as surface and bulk recombination rates) must be taken into account. Since the FEL has the typical temporal st ructure of a synchrotron radiation source and a flux comparable to the one obtainable at third generation storage rings, these results are o f relevance to the most advanced spectroscopic techniques used to stud y the electronic structure of semiconductors; therefore, in this paper we discuss the possible effects of intense synchrotron radiation beam s on position and lineshape of photoemission features at semiconductor surfaces. (C) 1998 Elsevier Science B,V. All rights reserved.